1. Field of the Invention
This invention relates to musical tone generation structures that are applicable to electronic musical instruments, particularly electronic pianos.
2. Description of the Related Art
In general, electronic pianos incorporate amplifiers and speaker systems for producing musical tones corresponding to musical tone signals being reproduced. It is an important problem for the electronic pianos to produce musical tones, which closely simulate actual piano sounds being actually produced by acoustic pianos. For this reason, engineers make every efforts to improve sound simulation techniques, particularly techniques of sound sources. In practice, it is very difficult to perfectly reproduce subtle nuances in the musical expression of acoustic pianos.
Through studies and experiments, we have reached a conclusion that the unique nuances in musical expression (or sound generation) of acoustic pianos are due to their tone-generation mechanisms. In acoustic pianos, hammers strike the strings to cause vibrations, which are transmitted to the soundboards via bridges. Thus, the soundboards vibrate to generate musical tones. Due to vibration of the soundboards, acoustic pianos (e.g., grand pianos) vibrate as a whole. Herein, musical tones are produced from both of an upper portion and a lower portion of the piano. The musical tones that are radiated from the upper portion of the piano are reflected by the top board (or reflector board), while the musical tones that are radiated from the lower portion of the piano are reflected by the floor. Then, the reflected musical tones are transmitted towards the audience by the air. It seems that the aforementioned operations play an important role in the formation of the nuances of the musical expression of acoustic pianos.
It is an object of the invention to provide a musical tone generation structure of an electronic musical instrument that is designed to closely reproduce the nuances of musical expression of an acoustic piano and the like.
In a first aspect of the invention, speakers are attached to a speaker attachment plate, which is installed inside of the casing and is arranged substantially horizontal in the normal use state of the electronic musical instrument, such that the front sides of the speakers are directed upwards. Sound release holes (or through holes) whose total area is larger than the total area of the speakers are formed to penetrate the bottom plate, which is arranged below the speaker attachment plate within the casing. In addition, enclosures are formed to enclose backsides (or rear sides) of the speakers attached to the speaker attachment plate.
In a second aspect of the invention, the enclosures are defined by the bottom plate and a side board that has a nonlinear circular arc shape in plan view. That is, two enclosures having different shapes in plan view are respectively formed in a left-side area and a right-side area within the casing below the speaker attachment plate. Thus, sounds radiated from the backsides of the speakers propagate downwardly through the enclosures and are further transmitted downwardly via the sound release holes toward the floor, on which the electronic piano is placed. Further, a reflector board whose one side can be lifted up and down is arranged above the speakers attached to the speaker attachment plate, and it is opened at a certain angle of inclination with respect to the horizontal plane corresponding to the top board of the electronic piano. Thus, the sounds radiated from the front sides of the speakers are reflected by the reflector board, similarly to acoustic pianos.
Further, the casing of the electronic piano as a whole vibrates in response to the vibrations emitted by the speakers that are driven in response to player""s performance on the keyboard of the electronic piano.
Thus, the electronic piano is capable of producing mixed sounds that contain first reflected sounds which are radiated from the front sides of the speakers and are reflected by the reflector board and second reflected sounds which are radiated from the backsides of the speakers, transmitted through the enclosures, and then reflected by the floor as well as additional sounds which are caused by the casing of the electronic piano due to the vibrations of the speakers.